The present invention relates to cellular confinement systems, in particular to three-dimensional cellular structures designed to physically confine soil, sand or other filler materials.
Confinement systems are commonly used in civil engineering applications for land reinforcement, erosion control, embankment stabilisation, retaining structures and channel protection. For example, metal or wicker baskets called gabions which are filled with stones, earth, etc. are used in the construction industry e.g. for shoring up, slopes or forming sea defences.
Cellular confinement systems prevent horizontal movement of the confined material, substantially improving the material shear strength and bearing capacity. They can be used to form access roads, hard standings, embankment slopes, containment dykes and levees, landfill lining and covers, dam faces and spillways, noise abatement walls and parking areas. Alternatively, such cellular systems can be stacked in order to support slopes or construct walls.
In industrial applications confinement cells are traditionally used as a lightweight filler within items to provide additional stiffness and strength. Cellular confinement structures also have military applications such as security and defence barriers.
Confinement systems formed from metal baskets are limited in their applications as the fill material must be large enough to be retained by the basket mesh. Gabions are typically filled with stone which is dressed and laid in the nature of wall so as to have an enhanced appearance when the baskets are left exposed to view. It can therefore be time consuming and labour intensive to provide a visually appealing system e.g. for shoring up an embankment adjacent to a motorway.
It has been proposed in WO 90/12160 to provide structural blocks formed by wire mesh cages which are lined with a geotextile material. By providing the cages with a fabric liner a wider variety of infill materials may be employed, such as soil and sand. However a liner needs to be stapled in place inside each cage. The system can be transported flat and then filled locally upon demand. However, such a composite system has certain drawbacks. Several manufacturing and assembly stages are required and the material cost is relatively high. The system is also relatively bulky and heavy to transport.
For civil engineering applications there are available cellular systems such as those manufactured by Terram Ltd. which are made from various grades of thermally bonded nonwoven geotextile. Such geotextiles have the flexibility of a fabric combined with a high tensile strength and stiffness. They are water permeable so soils are prevented from intermixing while still permitting water to flow freely through the system.
A cellular textile sheet is described in U.S. Pat. No. 4,572,705 and a three-dimensional cellular geotextile is described in FR 2824340.
Geotextile cellular systems can be used to confine all kinds of aggregates, soils, sand, etc. of any particle size. They are commonly used in a single layer to help prevent erosion by confining soil on slopes. Although such cellular systems can be stacked e.g. to form an earth retention structure for embankments, there is a limit to the steepness of wall that can be achieved. This depends on the fill material and cell size as well as the skill and accuracy of placement. Often, each subsequent layer of cells must be stepped back from the layer below in order to stabilise the structure. Using rock or aggregate fill materials a short vertical wall may be possible, but where the confined material is a fine granular fill material such as soil or sand it has been found that leakage occurs between the layers when the cells are stacked vertically. The strength of the system is also dictated by the properties of the geotextile material. In some applications additional reinforcement may be required.
The present invention seeks to mitigate the problems outlined above.